Method of processing lignified cellulose



Un State P te METHOD OF PROCESSING LIGNlFlE CELLULOSE Alfred M. Thomsen,265 Buckingham Way, Apt. 402,

. San Francisco 27, Calif.

The vegetable World furnishes us with substantially unlimited amounts oflignified cellulose. By this term I define the skeleton of mostvegetable structures which serves as the support, in part, for softertissues. While, obviously, it is best represented'when used by itself aswood it has many other forms. It is the aiin of my process to regard itas raw material for a chemical in dustry, not merely as structuralmaterial or as the source of paper pulp. In the instant case'thecellulose will be converted into well known solvents, the methoxylcontent of the lignin will appear as vanillin, the acetyl group'sassociated with both lignin and cellulose will become sodium acetate,and finally most of the'chemicals' used in elfecting suchtransformations will be recovered for reuse in the process.

I commence with a pulping operation, i.e., '1 separate the cellulose ascompletely as possible from the non-cellulose portion and then treateach fraction separately. Of all'conventional methods fordoing this thebest for my' purpbse is the so-called neutral sulphite cook as this hasthe least effect upon the cellulose portion. While soda is thebaseuniversally employed, potashcould be substituted so gin the claims, Iuse the term alkali or alkali metal as indicating either, or a mixtureof both.

The best way to describe my process is to follow the drawing in which Ihave represented what I will call a preferred version of my process andthen I will call attention ,to certain deviations therefrom. It will beobvious that certain parts of this composite operation could exist byitself, thus, if the object be to produce a good fiber, then the spentcooking liquor could be tre'ated as I indicate in the drawing, thusconstituting a recovery system for the neutral sulphite cook. Similarly,the solvents could be manufactured from any type of pulp. It is notessential that such deviations should be profitable, it would certainlybe workable. Hence, I regard all such modifications as within the scopeof my disclosure. Of course, as herein collectively represented, itforms what I regard as the best combination.

First, however, a word about the type of raw materials with which theprocess commences. On the drawing I have called it wood and that wouldbe correct if wood waste were involved. At the last end of any processfor the use of a tree there appears a waste? which has no use saveburning. In the pulp mill and the lumber mill this is a mixture of barkand sawdust, and at the end of the pulp mill it is the spent cookingliquor itself which is the waste. of course, it is always burnt in orderto recover, for re-us e, the resident soda salts and in such combustionthere is some salvage of heat.

But apart from the tree there is an endless succession of wastevegetable products that could serve as raw material for my process, fromsugar cane bagasse or the hold waste from the pineapple plantation, tothe ferns of the asparagus field. At best, any use made of such mate-vrial is as fuel, but in many cases vegetable wastes are destroyed, atthe place of origin, by fires, as the simplest solution. 7

In the drawing I show this wood as entering a saturator where it isthoroughly saturated with hot cooking liquor. It is then passed into thedigester where it is further heated to a temperature corresponding tothe gage pressure of about 175 lbs. This may be done on a batch basisbut I prefer a continuous operation-in Which the cooked material, pulpsuspended in spent cooking liquor, is continuously discharged through anozzle so that the escaping steam may be utilized as low-pressure steamin some other location, such as an evaporator. The time of cooking isthus determined by the time of residence in the digester. p p

In the blowpit, where the nozzle discharge is collected, the resultantpulp is next thoroughly Washed to free it from spent liquor, after whichit is converted into sugar in thesaccharifier. The process ofsaccharification consists of heating fora matter of minutes, only, untila Sepa'ration'is then partial conversion has taken place. made betweenliquid and solids and the solids are recycled to the sacoharificationstep until only a non-oellu-' lose residue is left, the latter beingsent to undergo the same treatment, described later on, to which thewhole of the spent cooking liquor is ultimately subjected. I prefer tohave said saccharifier operate as did the digester,

continuously, so that the evolved steam may be similarly utilized.

The time in the saccharifier is governed by performance,

i.e., the yield of sugar. The over-all efifect should be one pound ofsugar for each pound of cellulose, the increase in weight due to waterof hydration balancing the inevitable loss due to decomposition. Theactual saccharification is conventional, the acidity being equal to /2%of sulphuric acid and the temperature that corresponding to a gagepressure of pounds. These conditions are but an approximation and may bevaried at will by the operator in accordance with performance aspreviously explained under the factor of time. I p

The sugar solution thus produced is next treated in the conventionalmanner for the manufacture of that complex consisting of butyl alcohol,acetone, ethanol, carbon dioxide and hydrogen resulting from the lifefunction of Clostridium acetobutylicum, or its equivalents of whichseveral are well known. Obviously, it is first necessary to neutralizethe acid sugar solution to the preferred pH and to add nutrients for thepropagation of the added culture. I have shown the use of caustic sodabut that is pure medium which is absolutely sterile I can proceed in a Icontinuous manner so I have shown the broth advanced from fermenter tofermenter until in the last the sugar is virtually exhausted. Toequalize, therefore, I have also shown a continuous re-cycle of materialfrom the last fermenter to the first, a step on which the continuity ofthe operation largely depends. If due care be taken that no foreignculture be permitted to enter, the organism will function smoothly andthe violent evolution of gases so often encountered on a batch basiswill be largely eliminated.

Said gases, consisting of hydrogen and carbon dioxide are shown aspassing to the right hand side of the drawing where an advantageous useis found in the process itself, an advantage over conventional practiceWhere the synthesis of methanol is introduced as a substitutef The fullyfermented broth is then sent to a still where separation is made betweenthe overhead products and the Patented Dec. 13, 1960 bottoms. The latteris divided into two parts, one of which is re-cycled in place of washwater to the blowpit so that any non-used ingredients may be utilized.It is obvious that the saccharifying liquor in which the pulp issuspended becomes, in this manner, the still bottoms previouslydescribed;

Probably the greatest advantage in this type of recycling is representedby the use thus made of'the organisms abundantly represented, bothliving and dead. In the saccharification step there is thus not only theeffect of the acid and temperature on the cellulose but also on theprotoplasm of the bacteria. As a result, the correspond ing amino acidsof said protoplasm are set free as food for the organism in thefermentation step. This contributes amazingly to the speed at whichpropagation takes place as otherwise the organism would be compelled tomanufacture its own. It thus influences as well the temperature it isdesirable to maintain within the fermenters. While this, in general, issomewhere between 30 C. and 45 C. it will be varied by the operatoraccording to the actual performance of the entire system.

Having thus described the various steps by which the fermentation andsaccharification, per se, is much improved I will now show what happensto the spent liquor from the initial pulping step. In the digester,shown after the blowpit, an addition of caustic soda is made in such anamount that the total soda shall about equal the organics present. Thecharge is then held at a temperature corresponding to about 150 poundsgage pressure for about three hours and a large fraction of the methoxylcomponent of the lignin will have been converted into vanillin. Toextract this compound and to use the carbon dioxide-hydrogen mixture aswell, the digested material is cooled and then treated with this gaseousmixture in the device called a carbonator, which may be anything from asimple agitated tank to a bubble tower. Two purposes are thus servedsimultaneously. The caustic solution is neutralized, a necessary step toprecede vanillin extraction, and simultaneously, the gaseous mixtureloses much carbon dioxide and becomes correspondingly enriched inhydrogen, an equally necessary step in the further use of said hydrogen.

The carbonated material is next passed on to the extractor where it isthoroughly, progressively, extracted with the whole of the butyl alcoholfraction yielded by the still. Manifestly this is in an unrefinedcondition so two purposes are once more served. From the extractor thebutyl alcohol plus the extracted vanillin passes to the separator, whichis another still. Crude vanillin and the impurities of the butyl alcoholis thus obtained as one fraction, and refined butyl alcohol as anotherfraction.

The extracted material is next sent on to the fusionkettle, which is anyagitated evaporative device. Here it is commingled with additionalcaustic soda until the ratio of organics to soda shall be approximatelyas 1 is to 3. Evaporation is continued until the temperature of thefused mass shall approximate 230 C. and it is then sent to the leacher.While not shown in the drawing it is obvious that any butyl alcohol leftin the extracted material will have been volatilized by the rise intemperature and any methanol formed by the fusion step will likewisehave been volatilized. Naturally, these vapors will be condensed andrecovery of both methanol and butyl alcohol will be achieved.

In the leacher I have indicated the watery fluid in use as anotherportion of the still bottoms not used in the recycle step to theblowpit. Just enough will be used so as to remove the unused caustic andthe sodium acetate formed during the fusion in the form of a solution.This solution is, in turn, sent to an evaporator-crystallizer for thecrystallization of the sodium acetate, the mother liquor becoming a verystrong solution of caustic soda, which is returned as a re-cyclematerial to the vanillindigestion step and to the fusion step. Thissodium acetate forms a very valuable by-product. I have shown itsseparation from mother liquor by a centrifuge, which is optional.

From the leacher the residue is sent to a furnace which may be any typeof a metallurgical roaster. In this device, carbon is burned 01f,organic salts of soda converted to carbonates and any accidentallyformed sulphide is converted to sulphate. The ash leaving said furnacemay, therefore, be considered as a mixture of sulphate and carbonate ofsoda. I have shown that as received in a dissolver, which is but anotheragitated tank. The liquid used to dissolve the ash is, once more, a partof the still bottoms, already used twice before. I will here explain whyI elect to use this material in place of plain water. In view of thesulphuric acid added to the saccharification stage and the caustic sodaused to neutralize said acid before fermentation, said still-bottomsmust contain all such soda and acid previously added. This will be inthe form of sodium sulphate and by my consistent policy of re-cyclingthis sodium sulphate will eventually become converted into the sulphiterequired for digestion, thus making up at least in part for any lossesin the system. Obviously, it will be desirable to make the solution ofash as concentrated as possible but that is optional.

This solution of ash is next divided into two parts. One part iscausticized in the conventional manner with lime giving a solution ofcaustic soda with inert sodium sulphate which is re-cycled wherevercalled for, and a residual sludge of calcium carbonate. This latter iscommingled with the second part of the dissolved ash and with sulphurdioxide to form a solution of sodium sulphite and a precipitate ofcalcium sulphate. Separation is made between these substances, thecalcium sulphate discarded, and the solution of sodium sulphitere-cycled to the saturation step with which my process was commenced.Here I will add another step not shown on the drawing. Any shortage ofliquid at this point will be made up by re-cycling a portion of thespent cooking liquor, obtained from the blowpit, thus increasing thedensity of said spent liquor before and during all subsequent steps.

Another reason for my persistent re-cycling of dilute materials thatnormally go to waste but are recovered at no additional cost in mysystem will be found in the relatively small amounts of side-productsproduced along with the main items that I have already mentioned. Thus,

from every one hundred. grams of sugar consumed there is also producedabout 5% of acetic acid and rather less than one-half as much butyricacid. Inasmuch as the broth rarely contains more than 3% of availableproducts, all told, it is obvious that any plans of recovery would beabsurd. However, let us trace these minute commodities through myprocess. In the still-bottoms sent to the blowpit these commodities arereturned unchanged through the saccharification step. In neutralizing,they are converted to the corresponding soda salts and thus augment thepercentage present in the bottoms. Now when this enriched material isused in the leacher all such material ultimately comes out ascrystallized sodium acetate and/0r butyrate at the designated spot.Similarly, what is added to the dissolver is returned, in part, throughthe causticizing step to the same ultimate locus. It will also be simpleto trace all the remainder through the decomposer, the saturator, thedigester, the blowpit, until it finally has joined all the rest as acomponent of the spent liquor. When we consider that even the minuteamounts herein considered will ultimately mount up to nearly a hundredpounds of crystallized salts per ton of wood employed it is obvious thatit is not insignificant and that my process, in its entirety, is amethod of processing lignified cellulose, not a mere mixture ofunrelated factors. Similarly, the little ethanol represented on thedrawing, could be passed through thequick vinegar process to form adilute solution of acetic acid and then added to main, re-cycled flow,thus once more adding to the importance of the acetate-step as all suchtechnique, incorporated i in my process, would be inherently recoverieswithout additional cost. 1 i a Having thus proved that these diverseparts of my process do constitute a single, integrated process in orderto obtain optimum results, and having fully described my process,

Iclaim:

1. The method of processing lignified cellulose which comprises;saturating said lignified cellulose with a cooking liquor consistingessentially of a solution of neutral alkali metal sulphite and digestingsaid mixture under conventional conditions as to sulphite concentration,time, and temperature until said resident cellulose shall have beensubstantially liberated from incrusting substances; separating thecellulose portion from the spent cooking liquor, reserving said liquorfor future treatment; commingling the cellulose with a dilute acidmedium containing approximately /z% of sulphuric acid and heating atapproximately 150 pounds gage pressure to convert a portion of saidcellulose into the corresponding sugar; separating the residualcellulose from the sugar solution and recycling same into thesaccharification step until only a non-cellulose residue remains;neutralizing the resultant sugar solution and fermenting same with aculture suitable to the conversion of the sugar into volatile solventsrepresented principally by a mixture of butyl alcohol and acetone;distilling the fermented liquor to obtain volatile, overhead productsand relatively nonvolatile still-bottoms; separating the overhead intoits constituent parts; re-cycling the still-bottoms, in part, as theliquid portion of cellulose mixture undergoing saccharification and, inpart, as a dissolving medium in the further treatment of the reservedspent cooking liquor; commingling said spent liquor with suificientcaustic alkali until it shall approximately equal the total organicmaterial present and with the non-cellulose residual fromsaccharification and heating at a temperature corresponding to apressure of 150 lbs. gage until optimum conversion of the methoxylcontent therein into vanillin shall have been elfected; cooling andcarbonating the resultant liquor using for said carbonation the mixtureof carbon dioxide and hydrogen evolved during fermentation; extractingthe carbonated mass with the butyl alcohol fraction obtained in theprevious distillation step, and separating the solution of vanillin inbutyl alcohol from the extracted residue; commingling said extracted Iresidue with enough additional alkali metal hydroxide so that theadditive alkali shall be approximately 3 times that of the organicspresent and fusing the mixture until a terminal temperature ofapproximately 230 C. shall be obtained; leaching the resultant mass witha part of the previously obtained still-bottoms until substantially allthe unused alkali hydroxide and acetate, formed in the reaction, shallhave passed into solution in the leaching liquor; removing the alkaliacetate from the caustic liquor by crystallization and recycling theresultant mother liquor to the vanillin-digestion and fusion steps,respectively; roasting the residue from the leaching step to produce amixture of sulphate and carbonate of the contained alkali metal asanash; dissolving said ash in another portion of the still-bottomspreviously produced and dividing the resultant solution into two parts;causticizing one part with lime in the conventional manner to obtain thecaustic alkali required in the operations described and a calciumcarbonate sludge; commingling the latter with the other portion of thesolution of ash and with sulphur dioxide to produce calcium sulphate andalkali metal sulphite; separating the calcium sulphate and re-cyclingthe resultant solution of neutral alkali sulphite as the cooking liquorof the process.

2. The method of processing lignified cellulose which comprises;saturating said lignified cellulose with a cooking liquor consistingessentially of a solution of neutral alkali metal sulphite and digestingsaid mixture under 6 conventional conditions as to time, temperature,and sulphite concentration until said resident cellulose shall have beensubstantially liberated from encrusting substances; separating thecellulose portion from the spent cooking liquor; commingling the saidcellulose with an acid liquor containing approximately /z% of sulphuricacid, made by acidifying still-bottoms obtained in a later step, anddigesting for a partial saccharification only at a temperaturecorresponding to lbs. gage; separating the sugar solution formed fromun-reacted cellulose and recycling said cellulose to thesaccharification' step until only a non-cellulose residual shall remain;performing the saccharification in a continuous manner so that the sugarsolution, mixed with unreacted cellulose and residuum shall emergecontinuously as a jet from the saccharifying vessel; neutralizing theresultant sugar solution and fennenting it with a culture suited to theconversion of sugar, essentially, into butyl alcohol and acetone;performing said fermentation in a series of closed vessels to collectthe carbon dioxide and hydrogen formed during fermentation; passing thefermenting broth successively from vessel to vessel until in the lastvessel the sugar shall have been essentially converted, meanwhilere-cycling a portion of said fermenting material, continuously, from thelast vessel to the first vessel in the series; distilling the resultantliquor to obtain stillbottoms for re-cycling as herein prescribed, andan overhead product consisting essentially of butyl alcohol, acetone,and ethanol for subsequent separation and refining. 3. .The method ofprocessing lignified cellulose which comprises; saturating the lignifiedcellulose with a cooking liquor consisting essentially of a solution ofneutral alkali metal sulphite and digesting said mixture underconventional conditions as to sulphite concentration, time, andtemperature until the resident cellulose shall have been substantiallyliberated from the encrusting substances; performing said digestion in acontinuous manner so that the mixture of liberated cellulose and spentcooking liquor shall issue, continuously, in the form of a jet emergingfrom the digesting vessel; separating the liberated cellulose from thespent cooking liquor; commingling said spent liquor with suflicientalkali metal hydroxide that there shall be present approximately as muchsuch hydroxide as there is organic material; heating said mixture to atemperature corresponding to a pressure of about 150 pounds, gage, untiloptimum conversion of the resident methoxyl into vanillin shall havebeen obtained; carbonating the resultant material to liberate thevanillin thus produced; extracting the resultant material with butylalcohol and separating the solution of vanillin in butyl alcohol fromthe extracted residue; commingling said residue with suflicient additivealkali until said alkali shall be equal to approximately three times theamount of organics prwent and fusing the mixture until a finaltemperature of 230 C., approximately, shall have been obtained;condensing the vapors evolved in such fusion to recover butyl alcoholand methanol, the latter formed during said fusion; leaching theresultant mass with an aqueous liquid in sufiicient amount to extractsubstantially all of the unused caustic and of the alkali metal acetate,formed during fusion; evaporating the solution, crystallizing theresident acetate and separating it from the mother liquor, consistingessentially of caustic alkali, and re-cycling it to thevanillindigestion and fusion steps, respectively; roasting the residuefrom the leaching step to produce as an ash a mixture of sulphate andcarbonate of the contained alkali metal; dissolving said ash in a Wateryliquid and dividing into two parts; causticizing one part with lime inthe conventional manner to produce the caustic alkali required in theprocess, and a calcium carbonate sludge; commingling said sludge withthe remainder of the solution of ash and with sulphur dioxide to producea solution of alkali metal sulphite and a precipitate of 7 calciumsulphate; separating said calcium sulphate and 2,02%,087 recycling thesolution of alkali metal sulphite as the 2,123,211 cooking liquor of theprocess. 2,430,355 2,510,668 References Cited m the file of this patent5 UNITED STATES PATENTS 1,875,688 Christensen Sept. 6, 1932 1,904,589Wells Apr. 18, 1933 page 684.

8 Qu qhan D 3, 193 Sholler July 12, 1938 McCarthy Nov. 4, 1947 ThomsenJune 6, 1950 OTHER REFERENCES Fieser et al.: Organic Chemistry, 3rd ed.,1956,

2. THE METHOD OF PROCESSING LIGNIFIED CELLULOSE WHICH COMPRISES,SATURATING SAID LIGNIFIED CELLULOSE WITH A COOKING LIQUOR CONSISTINGESSENTIALLY OF A SOLUTION OF NEUTRAL ALKALI METAL SULPHITE AND DIGESTINGSAID MIXTURE UNDER CONVENTIONAL CONDITIONS AS TO TIME, TEMPERATURE, ANDSULPHITE CONCENTRATION UNTIL SAID RESIDENT CELLULOSE SHALL HAVE BEENSUBSTANTIALLY LIBERATED FROM ENCRUSTING SUBSTANCES, SEPARATING THECELLULOSE PORTION FROM THE SPENT COOKING LIQUOR, COMMINGLING THE SAIDCELLULOSE WITH AN ACID LIQUOR CONTAINING APPROXIMATELY 1/2% OF SULPHURICACID, MADE BY ACIDIFYING STILL-BOTTOMS OBTAINED IN A LATEX STEP, ANDDIGESTING FOR A PATRIAL SACCHARIFICATION ONLY AT A TEMPERATURECORRESPONDING TO 150 LBS. GAGE, SEPARATING THE SUGAR SOLUTION FORMEDFROM UN-REACTED CELLULOSE AND RECYCLING SAID CELLULOSE TO THESACCHARIFICATION STEP UNTIL ONLY A NON-CELLULOSE RESIDUAL SHALL REMAIN,PERFORMING THE SACCHARIFICATION IN A CONTINUOUS MANNER SO THAT THE SUGARSOLUTION, MIXED WITH UNREACTED CELLULOSE AND RESIDUUM SHALL EMERGECONTINUOUSLY AS A JET FROM THE SACCHARIFYING VESSEL, NEUTRALIZING THERESULTANT SUGAR SOLUTION AND FERMENTING WITH A CULTURE SUITED TO THECONVERSION OF SUGAR, ESSENTIALLY, INTO BUTYL ALCOHOL AND ACETONE,PERFORMING SAID FERMENTATION IN A SERIES OF CLOSED VESSELS TO COLLECTTHE CARBON DIOXIDE AND HYDROGEN FORMED DURING FERMENTATION, PASSING THEFERMENTING BROTH SUCCESSIVELY FROM VESSEL TO VESSEL UNTIL IN THE LASTVESSEL THE SUGAR SHALL HAVE BEEN ESSENTIALLY CONVERTED, MEANWHILERE-CYCLING A PORTION OF SAID FERMENTING MATERIAL, CONTINUOUSLY, FROM THELAST VESSEL TO THE FIRST VESSEL BOTTOMS FOR RE-CYLING AS HEREINPRESCRIBED, AND AN OVERHEAD PRODUCT CONSISTING ESSENTIALLY OF BUTYLALCOHOL, ACETONE, AND ETHANOL FOR SUBSEQUENT SEPARATION AND REFINING.